In some applications, it is desirable to mix the exhaust gases of a turbine engine with cooler air to reduce noise and infrared radiation generated by the turbine engine. For example, in military aircraft propelled by at least one gas turbine engine, it is desirable to reduce infrared radiation of the gas turbine engine in order to make the aircraft less vulnerable to common anti-aircraft weaponry which use infrared homing systems.
Previous efforts to suppress infrared radiation generated by a turbine engine have included the placement of mixing devices into the engine's exhaust path, such as the mixer disclosed in U.S. Pat. No. 6,606,854. However, these mixing devices are generally limited in their ability to operate at all ranges of engine performance and aircraft speeds. Thus, there is room for improvement in the art.
In some prior suppression systems, ambient air is admitted to the secondary via air inlet ducting in the vicinity of the engine compartment. As an aircraft achieves forward motion, the rate of airflow into the secondary air inlet ducting is a function of the aircraft's velocity, but since the secondary ducting is decoupled from the primary ducting system, engine compartment purge flow is not back-pressured. More advanced modern aircraft, particularly in military applications, may need to operate with effective infrared suppression and engine compartment purge flow across a wider range of engine performance. For example, vertical takeoff and landing (VTOL) or short takeoff and landing (STOL) aircraft require adequate infrared suppression during operations with low or even no forward velocity such as vertical takeoff, vertical landing, or hover operations.
A similar problem for VTOL, STOL, and other modern aircraft is the potential overpressurization of the engine compartment during high velocity flight. High forward velocity flight captures a high volume of ambient airflow into the air inlet ducting and a resultant higher stagnation pressure of the ambient air in the mixing region. If the differential pressure between the ambient air in the mixing region and the engine compartment becomes too great, then the engine compartment exhaust flow may have a resultant decrease in flow volume exiting the turbine engine compartment, creating a “stagnation” effect which can excessively heat engine components causing thermal failure and rendering infrared suppression ineffective.
While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the present disclosure is not intended to be limited to the particular forms disclosed. Rather, the present disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.